The present invention provides a bushing for a chain. More specifically, a roller-chain bushing has a relief zone provided in proximity to each of its edges, which relief zones are in areas to be compressed or compacted at press fitting of the bushing into an aperture of a bushing-link-plate along the pitch-line of the chain. The bushing-edge relief zone allows movement of bushing material to permit greater continuity and a consequent increase of the contact area between the link pin and the bushing, especially at initial contact between these two elements.
Roller chain assemblies generally utilize bushing-links and pin links with spaced apart apertures. A generally cylindrical bushing extends through a roller and between parallel bushing-links, which bushing is press fit into the juxtaposed apertures of the respective links. A pin extends through the bushing to secure the parallel link plates, roller and bushing to form a single link.
During assembly of the roller chain, the bushing is secured to the bushing link by press fitting it into the apertures of a bushing link. The as-formed bushings are generally a uniform cylinder, however, press fitting a bushing into the bushing-link holes or apertures deforms the cylinder ends. Bushing-end deformation results in deflection of the cylindrical shape, the inner diameter and the outer diameter of the bushing body, which resulted from the movement of material during press-fitting of the bushing ends. In an early effort to acconmmodate this material movement, material was removed from the bushing blank prior to roll-forming the bushing, which provided an opening or void in the bushing body to assimilate displaced material. This void may be considered as a degree of freedom for the central portion of the bushing. Thus, when the bushing cylinder ends are being deformed during the press fitting operation any movement of material along the bushing barrel-body would presumably be absorbed by the centrally positioned opening in the bushing body.
U.S. Pat. No. 2,424,087 to Focke et al. considered that smoother and denser surfaces of pitch holes in the side plates along with more tightly fit pins or bushings in those pitch holes provided greater fatigue resistance to the chain against failure by fracture of the side plates.
In another case, it had been indicated that press fitting the bushings into the holes induced residual compressive stress in the material surrounding the holes, which promoted increased fatigue resistance of the outer side plates. As a consequence, it was felt that the increased initial stress in the region of the bushing-receiving holes promoted increased fatigue resistance of the inner side plates. Further, U.S. Pat. No. 2,994,186 to Morrow asserted that utilizing a drift pin to cold work the region around the link plate holes both before and after heat treatment further increases the fatigue resistance of the link plates. The redrifting operation was used to produce improved fatigue resistance in the link plates and also to materially aid the extremely tight fits between the bushing and the link plate, which tight fits were considered to enhance the fatigue resistance of the link plates in the assembled chain.
Pressing a chain bushing into the pitch-holes of a bushing link compresses the bushing ends and alters the inner and outer diameter of the bushing. This alteration of the cylinder inner diameter is referred to in the industry as bushing collapse or barreling. As the chain operates, the pin bears, or should bear, against the inside wall of the bushing. As a result of the bushing collapse, the initial contact area between the pin and the bushing inner wall is limited to approximately point contact at the ends of the bushing where the inside diameter is at a minimum. The reduction of contact area between the pin and the bushing causes more rapid initial wear and elongation of the chain during operation.
Although the strength of the material surrounding the link hole may be enhanced by the mechanical working from the localized deformation experienced at press fitting of the bushing, the deformation of the bushing at its ends does not enhance the wear properties nor the fatigue properties of the chain. Rather, as noted above, the initial contact between the pin and the bushing is limited to a very small contact area within the bushing-link hole from the compression and deformation of the bushing at press fitting of the bushing and link. In one case, large deformation of the bushing-end deformation at press fitting into the bushing link has been avoided by rolling the edges of the unformed bushing blank to provide a tapered, or reduced, cross-sectional region at the bushing ends. The reduced cross-section avoids large compressive loads and bushing deformation during mating of the bushing and bushing link.
Changing the total circumference of the ends of the bushings manufactured from strip material requires an added and expensive operation, that is a separate strip rolling operation. The present invention eliminates the separate strip rolling operation by tapering the bushing blank only at its contact area with the pin along the pitch-line of the chain, which greatly reduces the amount of cold working required to achieve the needed taper. The taper may be provided by various methods, such as roll-forming the taper during blanking of the preform into the bushing or by coining, for example. Other exemplary cold working techniques include swaging, stamping or forging.